72 H. M, WOODCOCK. 



condition in Gregarines. Speaking- broadly^ further develop- 

 ment in tills order can be regarded as having taken place 

 alono' two distinct lines. In the one case, characteristic of 

 the great majority of Septate forms, the young growing para- 

 site penetrates only partially into the host-cell after attach- 

 ment,^ and remains in that position only during its early 

 growth.- For the rest of its trophic (and, of course, its sporo- 

 gonic) life the Gregariue is free in the gut. Concurrently 

 with the loss of the flagellum the parasite has developed the 

 peculiar gregarinoid movement (easily derivable from one of 

 a euglenoid nature) and, correlated with this, we find a marked 

 differentiation of the peripheral cytoplasm. 



The other line, that of the Monocystids, branched off early, 

 before the septum characterising most intestinal or Polycystid 

 Gregarines became developed. The young parasite, at the 

 besfinningf of its life, followed one of two courses. Either it 

 penetrated entii-ely into the host-cell and remained there for 

 a long time before falling into the gnt (e. g. Lankesteria 

 ascidife) or, on the other hand, it passed inwards between 

 the cells of the mucous membrane and came into intimate re- 

 lation with the connective tissue, etc., of the sub-mucosa, being, 

 as a rule, intercellular. In this latter manner have originated 

 the coelomic forms. In many cases (above described) these have 

 now, for the first time, lost their motility; in other words, 

 these coelomic Gregarines have developed a trophic condition 

 similar to that prevailing in the Coccidia, but quite apart and 

 independent from them. Neither on account of their habitat 

 nor because of the apparently simple nature of the sexual 

 process (see below, p. 79, et seq.) are the Monocystids to be 



' Tills question of attachment is very intercbting as regards its bearing upon 

 the Flagellate ancestry of I he order. Leger (21) has recently described 

 various parasitic Flagellates (Herpetomonas, Crithidia), characterised 

 by the possession of a gregariniform phase, in which the flagellum either 

 becomes greatly shortened and reduced, serving as au organ of attachment to 

 the epithelial cell of the host, or else disappears. 



^ In one or two instances (e. g. Stenophora) the sporozoite ))enetrates 

 completely into the cell, and the parasite remains intra-cellular until growth 

 is Qnished. This is, undoubtedly, a secondary and not a primitive condition. 



